C FZ3       SOURCE    CHAT      05/01/13    00:14:18     5004           
      FUNCTION FZ3(D,XA,XU,SQA,SQU,RSINT)                                       
      IMPLICIT INTEGER(I-N)
      IMPLICIT REAL*8 (A-H,O-Z)                                                 
      IF(RSINT.NE.0.D0) GOTO 2                                                  
1     FZ3=0.D0                                                                  
      RETURN                                                                    
2     FZ3=-RSINT*(ATAN((D*XA)/(RSINT*SQA))-ATAN((D*XU)/(RSINT*SQU)))            
      RETURN                                                                    
      END